Cadmium phytoavailability under greenhouse vegetable production system measured by diffusive gradients in thin films (DGT) and its implications for the soil threshold

• Published in: Environmental pollution (1987) 2018-10, Vol.241, p.412-421
• Main Authors: Tian, Kang, Xing, Zhe, Liu, Guoming, Wang, Huifeng, Jia, Mengmeng, Hu, Wenyou, Huang, Biao
• Format: Article
• Language: English
• Subjects: Cadmium - analysis; Cadmium - metabolism; Cd phytoavailability; China; Diffusive gradients in thin films (DGT); Greenhouse vegetable production; Metals; Soil - chemistry; Soil Pollutants - analysis; Soil Pollutants - metabolism; Soil threshold values; Vegetables - chemistry; Vegetables - metabolism
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2018.05.086

The diffusive gradients in thin films (DGT) technique is recognized to have advantages over traditional techniques. For example, the passive measurement generally follows the principle of metal uptake by plants, and its result incorporates the influences of soil properties, which may make DGT a good protocol for improving soil quality guidelines (SQGs). However, DGT has rarely been applied to assess Cd phytoavailability in soils under greenhouse vegetable production (GVP) systems. In this study, 29 turnips (Raphanussativus L.), 21 eggplants (Solanum melongena L.) and their corresponding soils were collected from GVP systems in Dongtai and Shouguang, eastern China. Simple linear regression and stepwise regression were performed using the soil Cd content and soil properties to predict the vegetable Cd content. Soil thresholds were derived based on both total and available Cd concentrations. The results showed that total Cd, DGT-measured Cd (DGT-Cd), soil-solution Cd (Soln-Cd) and CaCl2-extractable Cd (CaCl2-Cd) were all significantly correlated with vegetable Cd. DGT-Cd had the best correlation with turnip Cd. The total Cd threshold values ranged from 4.87 (pH 6.5) to 5.18 (pH 7.5) mg kg−1 for turnips and 14.60 (pH 6.5) to 14.90 (pH 7.5) mg kg−1 for eggplants. These Cd thresholds were higher than the current SQGs. The predicted of turnip Cd by DGT-Cd was not improved significantly by further considering the soil properties. The calculated soil threshold of DGT-Cd was 5.35 μg L−1 for turnips. However, the predicted soil threshold of DGT-Cd for eggplant was improved by including SOM, with R2 values from 0.53 to 0.70. The DGT-Cd threshold was calculated as 1.81 μg L−1 for eggplant (30.0 g kg−1 SOM). In conclusion, whether DGT measurements are independent of soil properties and preferable for the evaluation of Cd phytoavailability and the generation of soil thresholds remains to be clarified in future research. [Display omitted] •DGT-Cd could be used to predict the Cd phytoavailability to turnip and eggplant.•Both the total and available Cd contents were needed to derive the soil Cd threshold.•Vegetable Cd showed a significant correlation with the soil Cd:Zn ratio.•Whether DGT-Cd is independent of soil properties remains to be clarified. Phytoavailability and soil threshold values of Cd were established based on the DGT technique in collected soils under GVP systems.